Print train permitting accelerated printing speeds in a line printer

ABSTRACT

A print train of predetermined length and comprised of a plurality of type carrying blocks is provided with an increased number of hammer impactable type characters to thereby enable the realization of significantly accelerated printing speeds, the type blocks being individually and alternately driven to advance a toothed belt to which the blocks are separately coupled around a pair of rotatable sprockets, said accelerated printing speeds being realized without an accompanying degradation of printing quality resulting from the closer spacing of the adjacent characters, means being provided to shield the characters adjacent to an impacted character against the striking force of the hammer associated with such impacted character.

United States Patent Funk et al. Sept. 17, 1974 [5 PRINT TRAINPERMITTING 3,633,500 1/1972 Edwards 101 111 ACCELERATED PRINTING SPEEDSIN A 3,633,501 l/l972 Edwards 101/111 LINE PRINTER Inventors: John W.Funk, Plymouth; Eugene L.

Merlino, Jr., Dearborn Heights; Stephen Barasch, Westland; Daniel J.Woods, Plymouth, all'of Mich.

Burroughs Corporation, Detroit, Mich.

Filed: May 2, 1973 Appl. No.: 356,393

Assignee:

US. Cl. 101/111, 101/93 C Int. Cl B41j 7/06 Field of Search 101/93 C,111, 375, 269,

Ripple etal. 101/111 X Primary Examiner-Robert E. Pulfrey AssistantExaminerEdward M. Coven Attorney, Agent, or Firm-Edwin W. Uren; Paul W.Fish; Charles S. Hall [5 7 ABSTRACT A print train of predeterminedlength and comprised of a plurality of type carrying blocks is providedwith an increased number of hammer impactable type characters to therebyenable the realization of significantly accelerated printing speeds, thetype blocks being individually and alternately driven to advance atoothed belt to which the blocks are separately coupled around a pair ofrotatable sprockets, said accelerated printing speeds being realizedwithout an accompanying degradation of printing quality resulting fromthe closer spacing of the adjacent characters, means being provided toshield the characters adjacent to an impacted character against thestriking force of the hammer associated with such impacted character.

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PRINT TRAIN PERMITTING ACCELERATED PRINTING SPEEDS IN A LINE PRINTERBACKGROUND OF THE INVENTION Train printers of the type produced byBurroughs Corporation under style number B9247, and partially disclosedin U.S. Pat. No. 3,577,9l3 issued on May ll, 1971 to Herbert J. Hinze,may be characterized by the combination of a predetermined number oftype characters on individual type carrying blocks, the blocks beingremovably couplable to an internally toothed belt to form a print trainwhich is rotatably supported by a pair of spaced apart rotatablesprockets, the beltcoupled blocks not being otherwise interconnected. Intrain printers of this kind, rotation of the print train is accomplishedby driving means cooperating alternately with coupling means disposed onthe individual blocks, the alternate driving of the individual blocksserving to rotate the toothed belt around the rotatable sprockets and toabuttably push the downstream blocks in the direction of the sprockets,the blocks being separated from their abuttable relationship as they arepulled by the internal teeth of the belt around the peripheries of thesprockets. Train printers of this general character provide advantagesover prior art chain printers wherein the individual type characters arefixed to a belt or band, the band being rotated by driving means whichcooperates directly with at least one of the sprockets, the directattachment of the type characters to the band and the direct driving ofthe band by cooperable driving means having been found to presentvarious cost disadvantages in the areas of design and maintenance, andto present various operational disadvantages in the areas of type wearand band distortion.

A brief description of the construction and operation of the print traindescribed in detail in the abovereferenced patent is hereinafterpresented with refer ence to FIGS. 1 through 5. As shown in FIGS. 1 and5, an endless belt 3 having internal teeth 5 is rotatably supported by apair of rotatable and uprightly disposed sprockets 7 and 9, thelowermost portion of the belt representing an operative printingposition thereof, and the uppermost portion representing an inoperativeposition, rotation fo the belt by hereinafter described means serving toadvance the belt and particular areas thereof as between the operativeand inoperative positions. A predetermined number of type carryingblocks 11, shown in detached form in FIG. 2, and in coupled relationshipwith the belt 3 in FIGS. 1 and 5, are each comprised of an aperturedbelt receiving member 13 for receiving the outside surface of the belt3, and a plurality of offset and inwardly directed projections 15 forclampably receiving the inside surface of the belt and particularly therecesses formed by the internal teeth 5 thereof. Each of the typecarrying blocks 11 is additionally comprised of a plurality of externalteeth 17 extending outwardly from the belt receiving member 13, and anelongated type lug 19 normally disposed of the external'teeth l7 and thebelt receiving member 13, the type lug 19 presenting a type charactercarrying surface 21 having a plurality of type characters 23 integrallyformed thereon, the type lug 19 assuming a downwardly directed positionwhen the block 11 is assembled on the belt 3 and is located in theoperative position of the belt, as shown in FIG. 1. Each of the blocks11 is also provided with spacing pads 25 disposed on opposite sides ofthe type lug 19, the function thereof being to abuttably advance thedownstream blocks to the sprocket 7, and from the sprocket 7 to thesprocket 9 when a given block 11 is drivably advanced by hereinafterdescribed means. The type carrying blocks llare assembled on the belt 3as illustrated in FIG. 3, it being noted from FIG. 3 that the belt iswider than the sprockets 7 and 9, and that the offset and inwardlydirected projections 15 of the blocks engage opposite portions of thebelt which extend outwardly from the sprockets (as identified at 27 inFIG. 3), each block being coupled to the belt 3 with minimal linear playas permitted by the relative dimensions of the recesses between theteeth 5 of the belt and the projections 15 of the blocks.

With the plurality of type carrying blocks 11 coupled to the belt 3, theprint train so formed is continuously rotatable about the sprockets 7and 9 to thereby bring selected type characters 23 into impactreceivingrelationship with a plurality of linearly arranged columnidentifyinghammers 29, the print train being rotated in a counterclockwisedirection (as viewed in FIG. 1) through the driving cooperation of adrive gear 31 fixed to a drive shaft 33 (as best illustrated in FIG. 4).Rotation of the drive gear 31 and the peripheral teeth 35 thereof iseffective to alternately engage the external teeth 17 of the typecarrying blocks 1 l to thereby alternately advance each block 11 in thedirection of the downstream sprocket 7, the blocks 11 located betweenthe driven block and the sprocket 7 being abuttably pushed to thesprocket through contact of the spacing pads 25 of the various blocks,movement of the driven blocks being transmitted to the belt by means ofthe hereinbefore described engagement of the projections 15 with theoverhanging toothed portions 27 of the belt. Engagement of the drivegear 31 with the external teeth 17 of the individual blocks 11, and thepushing effect of the driven blocks on the downstream blocks can best beunderstood with reference to FIG. 4. FIG. 5 is illustrative of themanner in which the movement of the belt 3 serves to pull the blocks 11around the sprockets 7 and 9, it being noted that the abuttingrelationship between the blocks is removed during such circularmovement. It can be seen from FIG. 5 that the leading edges of theprojections 15 of the blocks 11 that are being moved in the direction ofthe sprockets 7 and 9 are in contact with the trailing edges of theedges of the internal teeth 5 of the belt 3, the movement of such blocksserving to transmit rotational motion to the belt 3, whereas thetrailing edges of the projections 15 of the blocks being moved aroundthe sprockets 7 and 9 are in contacting relationship with the leadingedges of the internal teeth 5, the moving belt 3 accordingly serving topull the blocks 11 around the sprockets.

Known train printers of the type produced by Burroughs Corporation understyle number B9247 have commonly provided or 132 linearly arrangedimpactable hammers 29, and 48 type carrying blocks 11 disposed along theprint train, each of the blocks 11 being provided with four typecharacters 23, as shown in FIG. 2, presenting a total of 192 selectabletype characters arranged along the belt 3. With a print train rotatingspeed of 170.66 inches per second, a printing throughput of from 440 to1,200 lines per minute has been achieved, depending upon the characterset employed, a 750 lines per minute throughput being achieved with a 48character set, and with proportionately higher and lower throughputspeeds with smaller and larger character sets, respectively. As is wellknown in the line printer art, increased printing throughput may beachieved with a given character set by increasing the total number oftype characters disposed along the print train, or alternatively,through the employment of smaller character sets that permit increasedrepetition of the individual characters comprising the set.

With the increased processing speeds of present generation computers,continued attention is given to the development of ways and means ofincreasing the throughput speeds of input and output peripheralscomprising data processing systems, and particularly to ways and meansof increasing the throughput speeds of line printers. Since theemployment of smaller character sets would present serious limitationsto printing flexibility, attention has been focused on ways and means ofincreasing the total number of characters along the print train, as byincreasing the number of type characters per block from 4 to 6, thetotal number of characters provided by the 48 type blocks being thusincreased from 192 to 288. Early experimentation with this approach, inan effort to achieve a printing throughput of 1,000 lines per minutewith a 48 character set, resulted in the ghost printing of typecharacters adjacent to the characters that were impacted by the hammers29, as illustrated in FIG. 6 wherein the printed characters 37 on themedia are accompanied by ghost characters 39. Investigation into thecause of such ghost printing revealed a tendency of a hammer 29 (FIG. 1when impacted against a selected type carrier 23, to advance the mediainto light printing contact with the type characters adjacent to theselected character, the tendency being aggravated proportionally to anincrease in the stiffness of the media and to a reduction in the spacebetween the type characters on the blocks 11.

SUMMARY OF THE INVENTION It is accordingly an object of the presentinvention to significantly increase the printing throughput of trainprinters of the above characterized type, as from 750 lines per minuteto 1,050 lines per minute in the case of the Burroughs train printer,such increase in speed to be achieved with a 48 character set.

It is a further object of the present invention to achieve thissignificant increase in printing throughput without altering theover-all dimensions of the printer, and without changing the number andsize of the type carrying blocks that are disposed along the print trainthereof.

It is yet a further important object of the present invention to providefor such significant increase in printing throughput without degradingthe quality of the printed result, as by the entertainment of ghostprinting of the kind illustrated in exaggerated form in FIG. 6.

Yet another object of the present invention is to provide a print trainwherein the pitch distance between the type characters is significantlydecreased, and wherein each type carrying block is provided with meanseffective for preventing a printing contact as between the media and thetype characters adjacent a selected type character when the selectedtype character is impacted by its associated hammer.

BRIEF DESCRIPTION OF THE DRAWING The drawing figures accompanying thepresent specification, hereinafter described,are presented as an aid tounderstanding the general character of train printers, to comprehendingthe nature of the problem that is customarily encountered in attemptingto achieve significantly increased throughput speeds therewith, and toconveying a lucid explanation of the solution to the problem ascontemplated by the inventors.

FIG. 1 is a rear elevational view of a print train employed in lineprinters of the train type;

FIG. 2 is a front view of a type carrying block of the kind comprisingthe print train of FIG. 1, such block being provided with theconventional number of four type characters disposed on a type carryingsurface thereof;

FIG. 3 is a sectional view of a type carrying block assembled on thebelt and in engaged relationship with one of the sprockets;

FIG. 4 is a bottom view of the mechanism of FIG. 1;

FIG. 5 is a partial sectional view of the print train of FIG. 1 inassociation with one of the sprockets;

FIG. 6 is an enlarged and exaggerated sample of a printed result showingthe ghost printing of characters on the media intermediate the intendedprinted characters;

FIG. 7 is an enlarged sample of the desired printed result on the media;

FIG. 8 is a front view of the inventive type carrying block showing sixtype characters arranged along the type carrying surface thereof andwith barriers interposed between the characters; and

FIG. 9 is a perspective view of the type carrying surface of theinventive block of FIG. 8, showing the six type characters with barriersinterposed therebetween.

DESCRIPTION OF THE PREFERRED EMBODIMENT The objective of increasing theprinting throughput of the above referenced train printer from 750 to1,050 lines per minute, based on a 48 character set, without alteringthe dimensions of the print train or the number or size of the typecarrying blocks 11 carried by the belt 3, led to the development of thetype carrying block 1 1' shown in FIG. 8, 48 of such blocks beingarranged along the belt 3 with each block containing a total of six typecharacters 23, the type characters accordingly being spaced in closerproximity to one another. The effect of this increase of two typecharacters per block resulted in an increase in the total number of typecharacters in the print train from 192 to 288, such increased number oftype characters permitting a multiplied repetition thereof along thebelt 3 to thereby provide the desired increase in printing throughput.With the resultam decreased spacing between the type characters on theindividual blocks 11', the inventive blocks were additionally providedwith barriers 41 disposed between the type characters 23, such barriers,being of substantially equal height to the height of the type characters23 extendiing outwardly from the type lugs 19, serving to support themedia upon impacting of a hammer 29 against a selected type character 23to thereby prevent the media from being moved into printable contactwith the type character adjacent the selected character.

The barriers 41 may present a substantially flat raised surface betweenthe type characters as illustrated in FIG. 9, or provided with aslightly radiused raised surface depending upon the relative stiffnessof the media to be used and the corresponding adjacent characters.

What is claimed is:

1. An improved rotatably supported print train operatively associatedwith a plurality of linearly arranged selectively impactable hammers ina printing device and responsive to driving means of said printingdevice to bring selected type characters into printing position relativeto said hammers for producing printed characters on printable media ofvarying rigidity, said print train comprising:

a. an endless toothed belt encompassing a pair of spaced-apart sprocketsproviding said rotatable support for said print train,

b. a predetermined plurality of type carrying blocks distributed alongand removably coupled to said endless belt in engaged relationshiprelative to the teeth thereof, each of said blocks having a plurality ofexternal teeth disposed on an edge thereof and in cooperablerelationship relative to said driving means to be intermittentlyadvanced thereby so as to rotate said belt around said sprockets, a typelug presenting a type carrying surface contiguous to and normallydisposed of said external teeth, and a plurality of spaced-apart typecharacters arranged along said type carrying surface in close proximityto one another and effective for producing said printed characters onsaid printable media of said varying rigidity upon the impacting ofselected hammers thereagainst, and media supporting means fixed to saidtype carrying surfaces of said type lugs and effective for preventingthe printing of ghost characters on printable media of relativelygreater rigidity such as would result from said close proximity of saidtype characters on said type carrying surfaces, said media supportingmeans comprising an elongated barrier fixed to and transversely disposedof said type carrying surface of each of said type lugs intermediateadjacent pairs of said type characters thereof, each of said barriersextending outwardly from the type lug to which it is fixed by a distancesubstantially equal to the extension of said adjacent type characterstherefrom, whereby said printable media is held away from the typecharacters oppositely adjacent to a selected type character whenactivated into printable contact with said selected character uponimpacting of the hammer associated therewith.

2. An improved printing mechanism for producing printed characters onprintable media of varying rigidity comprising:

a. a media guideway,

b. means for advancing said media along said guidec. a plurality ofselectively impactable hammers transversely disposed on one side of saidmedia guideway,

d. a rotatably supported endless print train associated with drivingmeans of said printing mechanism and transversely and normally disposedrelative to said media guideway on the opposite side thereof from saidplurality of hammers, said print train having a predetermined pluralityof type character carrying blocks arranged therealong such that therotation of said print train by said driving means is effective totransport said blocks as between an operative position thereofcontiguous to said guideway and said hammers and an inoperative positionthereof remote from said guideway and said hammers, each of said blocksincluding a plurality of external teeth disposed along an edge thereofand in cooperable relationship relative to said driving means to beintermittently advanced thereby so as to rotate said print train aroundsaid rotatable support thereof, a type lug presenting a type charactercarrying surface contiguous to and normally disposed of said externalteeth, a plurality of spaced-apart type characters arranged along saidtype character carrying surface in close proximity to one another andeffective for producing said printed characters on said printable mediaof said varying rigidity upon the impacting of selected hammersthereagainst, and

e. media supporting means fixed to said type character carrying surfacesof said type lugs and effective for preventing the printing of ghostcharacters on printable media of relatively greater rigidity such aswould result from said close proximity of said type characters on saidtype carrying surfaces, said media supporting means comprising anelongated barrier fixed to and transversely disposed of said typecharacter carrying surface of each of said type lugs intermediateadjacent pairs of said type characters thereof, each of said barriersextending outwardly from the type lug to which it is fixed by a distancesubstantially equal to the extension of said adjacent type characterstherefrom, whereby said media is held away from the type charactersoppositely adjacent to a selected type character when activated intoprintable contact with said selected character upon impacting of thehammer associated therewith.

3. An improved type character carrying block for use in a predeterminedplurality in an endless rotatably mounted print train in a printingdevice for producing printed characters on printable media of varyingrigidity, said print train having an endless toothed belt disposed inencompassing relationship with a pair of spaced-apart rotatablesprockets, said belt being effective for removably coupling saidpredetermined plurality of type character carrying blocks theretorelative to the teeth thereof, said printing device having media guidingand advancing means, a predetermined plurality of impactable hammerstransversely arranged relative to the direction of advancement of themedia, and print train driving means effective for rotating said beltand said blocks to thereby advance selected type characters intoprintable relationship with said hammers, said improved type carryingblock comprising:

a. a plurality of external teeth disposed along an edge thereof and incooperable relationship relative to said driving means to beintermittently advanced thereby so as to rotate said belt around saidpair of sprockets,

b. a type lug presenting a type character carrying surface contiguous toand normally disposed of said external teeth,

0. a plurality of spaced-apart type characters arranged along said typecharacter carrying surface in close proximity to one another andeffective for producing said printed characters on said printable mediaof said varying rigidity upon the impacting of selected hammersthereagainst, and

d. media supporting means fixed to said type character carrying surfaceof said type lug and effective for preventing the printing of ghostcharacters on printable media of relatively greater rigidity such aswould result from said close proximity of said characters on said typecharacter carrying surface, said media supporting means comprising anelongated barrier fixed to and transversely disposed of said typecharacter carrying surface of said type lug intermediate adjacent pairsof said type characters thereof, each of said barriers extendingoutwardly from the type lug by a distance substantially equal to theextension of said adjacent type characters therefrom, whereby saidprintable media is held away front the type characters oppositelyadjacent to a selected type character when activated into printablecontact with said selected character upon impacting of the hammerassociated therewith.

4. An improved type carrying block for multiple use in association witha rotatably mounted and driven endless internally toothed belt to definea print train of a printing device having selectively impactablehammers, said printing device being effective for producing printedcharacters on printable media of varying rigidity, said blockcomprising:

a. an apertured belt receiving member presenting a flat orthogonalsurface for receiving the outside surface of said belt, said memberadditionally presenting, within the framework of the aperture thereof, aplurality of oppositely'disposed offset and inwardly directedprojections, said projections being effective for clampably receivingthe inside surface of said belt and particularly for engageablyreceiving recesses formed by said internal teeth thereof, a

b. a plurality of external teeth substantially disposed in coplanarrelationship with said belt receiving member, said external teeth beingresponsively effective for driving said belt and said print train,

'c. an elongated type lug parallelly disposed relative to said beltreceiving member and normally disposed relative to said external teeth,said type lug presenting a type character carrying surface having aplurality of spaced-apart type characters integrally formed thereon inclose proximity to one another, said type characters being effective forproducing said printed characters on said printable media of saidvarying rigidity upon the impacting of selected hammers thereagainst,said type character carrying surface having also a plurality ofelongated media supporting barriers transversely disposed relativethereto and intermediate adjacent pairs of said type characters, saidbarriers being effective for preventing the printing of ghost characterson printable media of relatively greater rigidity such as would resultfrom said close proximity of said type characters on said type charactercarrying surface, each of said barriers extending outwardly from thetype lug by a distance substantially equal to the extension of saidadjacent type characters therefrom, whereby said printable media is heldaway from the type characters oppositely adjacent to a selected typecharacter when activated into printable contact with said selectedcharacter upon impacting of the hammer associated therewith.

1. An improved rotatably supported print train operatively associated with a plurality of linearly arranged selectively impactable hammers in a printing device and responsive to driving means of said printing device to bring selected type characters into printing position relative to said hammers for producing printed characters on printable media of varying rigidity, said print train comprising: a. an endless toothed belt encompassing a pair of spaced-apart sprockets providing said rotatable support for said print train, b. a predetermined plurality of type carrying blocks distributed along and removablY coupled to said endless belt in engaged relationship relative to the teeth thereof, each of said blocks having a plurality of external teeth disposed on an edge thereof and in cooperable relationship relative to said driving means to be intermittently advanced thereby so as to rotate said belt around said sprockets, a type lug presenting a type carrying surface contiguous to and normally disposed of said external teeth, and a plurality of spaced-apart type characters arranged along said type carrying surface in close proximity to one another and effective for producing said printed characters on said printable media of said varying rigidity upon the impacting of selected hammers thereagainst, and c. media supporting means fixed to said type carrying surfaces of said type lugs and effective for preventing the printing of ghost characters on printable media of relatively greater rigidity such as would result from said close proximity of said type characters on said type carrying surfaces, said media supporting means comprising an elongated barrier fixed to and transversely disposed of said type carrying surface of each of said type lugs intermediate adjacent pairs of said type characters thereof, each of said barriers extending outwardly from the type lug to which it is fixed by a distance substantially equal to the extension of said adjacent type characters therefrom, whereby said printable media is held away from the type characters oppositely adjacent to a selected type character when activated into printable contact with said selected character upon impacting of the hammer associated therewith.
 2. An improved printing mechanism for producing printed characters on printable media of varying rigidity comprising: a. a media guideway, b. means for advancing said media along said guideway, c. a plurality of selectively impactable hammers transversely disposed on one side of said media guideway, d. a rotatably supported endless print train associated with driving means of said printing mechanism and transversely and normally disposed relative to said media guideway on the opposite side thereof from said plurality of hammers, said print train having a predetermined plurality of type character carrying blocks arranged therealong such that the rotation of said print train by said driving means is effective to transport said blocks as between an operative position thereof contiguous to said guideway and said hammers and an inoperative position thereof remote from said guideway and said hammers, each of said blocks including a plurality of external teeth disposed along an edge thereof and in cooperable relationship relative to said driving means to be intermittently advanced thereby so as to rotate said print train around said rotatable support thereof, a type lug presenting a type character carrying surface contiguous to and normally disposed of said external teeth, a plurality of spaced-apart type characters arranged along said type character carrying surface in close proximity to one another and effective for producing said printed characters on said printable media of said varying rigidity upon the impacting of selected hammers thereagainst, and e. media supporting means fixed to said type character carrying surfaces of said type lugs and effective for preventing the printing of ghost characters on printable media of relatively greater rigidity such as would result from said close proximity of said type characters on said type carrying surfaces, said media supporting means comprising an elongated barrier fixed to and transversely disposed of said type character carrying surface of each of said type lugs intermediate adjacent pairs of said type characters thereof, each of said barriers extending outwardly from the type lug to which it is fixed by a distance substantially equal to the extension of said adjacent type characters therefrom, whereby said media is held away from the type characters oppositely adjacent to a selected type character when Activated into printable contact with said selected character upon impacting of the hammer associated therewith.
 3. An improved type character carrying block for use in a predetermined plurality in an endless rotatably mounted print train in a printing device for producing printed characters on printable media of varying rigidity, said print train having an endless toothed belt disposed in encompassing relationship with a pair of spaced-apart rotatable sprockets, said belt being effective for removably coupling said predetermined plurality of type character carrying blocks thereto relative to the teeth thereof, said printing device having media guiding and advancing means, a predetermined plurality of impactable hammers transversely arranged relative to the direction of advancement of the media, and print train driving means effective for rotating said belt and said blocks to thereby advance selected type characters into printable relationship with said hammers, said improved type carrying block comprising: a. a plurality of external teeth disposed along an edge thereof and in cooperable relationship relative to said driving means to be intermittently advanced thereby so as to rotate said belt around said pair of sprockets, b. a type lug presenting a type character carrying surface contiguous to and normally disposed of said external teeth, c. a plurality of spaced-apart type characters arranged along said type character carrying surface in close proximity to one another and effective for producing said printed characters on said printable media of said varying rigidity upon the impacting of selected hammers thereagainst, and d. media supporting means fixed to said type character carrying surface of said type lug and effective for preventing the printing of ghost characters on printable media of relatively greater rigidity such as would result from said close proximity of said characters on said type character carrying surface, said media supporting means comprising an elongated barrier fixed to and transversely disposed of said type character carrying surface of said type lug intermediate adjacent pairs of said type characters thereof, each of said barriers extending outwardly from the type lug by a distance substantially equal to the extension of said adjacent type characters therefrom, whereby said printable media is held away front the type characters oppositely adjacent to a selected type character when activated into printable contact with said selected character upon impacting of the hammer associated therewith.
 4. An improved type carrying block for multiple use in association with a rotatably mounted and driven endless internally toothed belt to define a print train of a printing device having selectively impactable hammers, said printing device being effective for producing printed characters on printable media of varying rigidity, said block comprising: a. an apertured belt receiving member presenting a flat orthogonal surface for receiving the outside surface of said belt, said member additionally presenting, within the framework of the aperture thereof, a plurality of oppositely disposed offset and inwardly directed projections, said projections being effective for clampably receiving the inside surface of said belt and particularly for engageably receiving recesses formed by said internal teeth thereof, b. a plurality of external teeth substantially disposed in coplanar relationship with said belt receiving member, said external teeth being responsively effective for driving said belt and said print train, c. an elongated type lug parallelly disposed relative to said belt receiving member and normally disposed relative to said external teeth, said type lug presenting a type character carrying surface having a plurality of spaced-apart type characters integrally formed thereon in close proximity to one another, said type characters being effective for producing said printed characters on said printable media of said varyiNg rigidity upon the impacting of selected hammers thereagainst, said type character carrying surface having also a plurality of elongated media supporting barriers transversely disposed relative thereto and intermediate adjacent pairs of said type characters, said barriers being effective for preventing the printing of ghost characters on printable media of relatively greater rigidity such as would result from said close proximity of said type characters on said type character carrying surface, each of said barriers extending outwardly from the type lug by a distance substantially equal to the extension of said adjacent type characters therefrom, whereby said printable media is held away from the type characters oppositely adjacent to a selected type character when activated into printable contact with said selected character upon impacting of the hammer associated therewith. 